1. Field of the Invention
The invention relates to a direct type backlight module; in particular, the invention relates to a direct type backlight module that enhances light uniformity.
2. Description of the Related Art
In the display unit of a liquid crystal display, a backlight module is generally utilized as a light source. Depending on the structure, the backlight module can be an edge type or a direct type. Since this invention seeks to improve the direct type backlight module, the description of the edge type backlight module is omitted.
As shown in FIG. 1, a direct type backlight module 10 includes a frame 11, a reflector 12, a plurality of lamps 13, a diffuser plate 14, a prism sheet 15, a diffuser sheet 16, and a liquid crystal panel 17. The reflector 12 is disposed in the frame 11 and is located at the bottom of the direct type backlight module 10, and reflects light from the lamps 13 out of the backlight module 10. The lamps 13 are utilized as the light source of the direct type backlight module 10. The diffuser plate 14 is disposed on the reflector 11 in such a manner that the lamps 13 are covered by the diffuser plate 14, and enhance the brightness of the front side of the backlight module 10. The prism sheet 15, the diffuser sheet 16, and the liquid crystal panel 17 are disposed on the diffuser plate 14.
The direct type backlight module 10, however, has the following disadvantage. To uniformly distribute light from the backlight module 10, a plurality of print dots (inks) 141 are generally printed on the diffuser plate 14. Part of the light may be absorbed by the print dots, and part of the light may be reflected back to the reflector 12. Thus, the light-utilization efficiency of the entire backlight module suffers.
In Japanese Publication No. 2001-356702, a direct type backlight module 20 that solves the above problem is disclosed. As shown in FIG. 2, two diffuser plates 22, 23 are disposed above the lamps 21, and an air layer 24 is formed between the diffuser plates 22, 23. Specifically, in the direct type backlight module 20, an additional diffuser plate is disposed to enhance the light uniformity. The disadvantage of the backlight module 20 is that an additional diffuser plate can diffuse the light, but cannot actually guide the light to the front side of the backlight module. Thus, light uniformity is not enhanced.